1. Field of the Invention
This invention relates to a damaged assessment system for plastic structures and more particularly to a damage assessment system for fiber reinforced plastic structures having a three-dimensional optical fiber grid as an integral part of the structure.
2. Description of the Prior Art
Fiber reinforced plastic (FRP) composite materials, such as glass reinforced plastics (GRP), are increasingly being used for structural applications due to their attractive material properties, such as high strength and stiffness to weight ratios. In some applications, the structure may be of considerable size, with a large projecting surface area which is prone to various kinds of mechanical damage. To insure the structural integrity of these structures, it is important to nondestructively inspect them during their service life.
However, in applications, such as sonar domes on submarines, inspection is an inconvenient and time-consuming operation. It usually requires that the vessel cease operations to perform the tests, which is a distinct disadvantage for a military ship on patrol. Visual inspection is not always accurate since an impact may cause internal damage to the material, such as delamination, which is not apparent from the outer surface. Hand held ultrasonic units for scanning may be used, but are very time consuming and not definitive. Since sonar domes are particularly vulnerable to foreign object impact, and since its integrity is vital to the mission of the ship, present inspection methods of FRP sonar domes are inadequate to allow military ships to function on patrol as required. Likewise, in other applications, inspection methods are time consuming, expensive, and not accurate.